2 * Compressed RAM block device
4 * Copyright (C) 2008, 2009, 2010 Nitin Gupta
6 * This code is released using a dual license strategy: BSD/GPL
7 * You can choose the licence that better fits your requirements.
9 * Released under the terms of 3-clause BSD License
10 * Released under the terms of GNU General Public License Version 2.0
12 * Project home: http://compcache.googlecode.com
18 #include <linux/spinlock.h>
19 #include <linux/mutex.h>
24 * Some arbitrary value. This is just to catch
25 * invalid value for num_devices module parameter.
27 static const unsigned max_num_devices
= 32;
30 * Stored at beginning of each compressed object.
32 * It stores back-reference to table entry which points to this
33 * object. This is required to support memory defragmentation.
41 /*-- Configurable parameters */
43 /* Default zram disk size: 25% of total RAM */
44 static const unsigned default_disksize_perc_ram
= 25;
47 * Pages that compress to size greater than this are stored
48 * uncompressed in memory.
50 static const unsigned max_zpage_size
= PAGE_SIZE
/ 4 * 3;
53 * NOTE: max_zpage_size must be less than or equal to:
54 * XV_MAX_ALLOC_SIZE - sizeof(struct zobj_header)
55 * otherwise, xv_malloc() would always return failure.
58 /*-- End of configurable params */
60 #define SECTOR_SHIFT 9
61 #define SECTOR_SIZE (1 << SECTOR_SHIFT)
62 #define SECTORS_PER_PAGE_SHIFT (PAGE_SHIFT - SECTOR_SHIFT)
63 #define SECTORS_PER_PAGE (1 << SECTORS_PER_PAGE_SHIFT)
65 /* Flags for zram pages (table[page_no].flags) */
67 /* Page is stored uncompressed */
70 /* Page consists entirely of zeros */
76 /*-- Data structures */
78 /* Allocated for each disk page */
82 u8 count
; /* object ref count (not yet used) */
84 } __attribute__((aligned(4)));
87 u64 compr_size
; /* compressed size of pages stored */
88 u64 num_reads
; /* failed + successful */
89 u64 num_writes
; /* --do-- */
90 u64 failed_reads
; /* should NEVER! happen */
91 u64 failed_writes
; /* can happen when memory is too low */
92 u64 invalid_io
; /* non-page-aligned I/O requests */
93 u64 notify_free
; /* no. of swap slot free notifications */
94 u32 pages_zero
; /* no. of zero filled pages */
95 u32 pages_stored
; /* no. of pages currently stored */
96 u32 good_compress
; /* % of pages with compression ratio<=50% */
97 u32 pages_expand
; /* % of incompressible pages */
101 struct xv_pool
*mem_pool
;
102 void *compress_workmem
;
103 void *compress_buffer
;
105 spinlock_t stat64_lock
; /* protect 64-bit stats */
106 struct mutex lock
; /* protect compression buffers against
107 * concurrent writes */
108 struct request_queue
*queue
;
109 struct gendisk
*disk
;
111 /* Prevent concurrent execution of device init and reset */
112 struct mutex init_lock
;
114 * This is the limit on amount of *uncompressed* worth of data
115 * we can store in a disk.
117 u64 disksize
; /* bytes */
119 struct zram_stats stats
;
122 extern struct zram
*devices
;
123 extern unsigned int num_devices
;
125 extern struct attribute_group zram_disk_attr_group
;
128 extern int zram_init_device(struct zram
*zram
);
129 extern void zram_reset_device(struct zram
*zram
);